1. Field of the Invention
The invention relates to a method of a gate oxide layer treatment, and more particular to a fabricating method for improving hot carrier degradation.
2. Description of the Related Art
The major function of silicon oxide layer formed using oxidation in semiconductor fabrication process is to be used as a gate oxide layer in metal-oxide-semiconductor (MOS) devices. Since the electrical characteristic of the gate oxide layer affects the quality of the MOS tremendously, too much dopant or charge changes the threshold voltage of on/off switches in MOS devices. Moreover, the breakdown voltage is lowered, and the "time-dependent dielectric breakdown (TDDB)" associated with the product reliability is degraded (that is, the lifetime is shortened).
To enhance the reliability of the gate oxide layer, a conventional method of nitridizing an oxide layer, for example, heating in a furnace or rapid thermal annealing in a nitrogen or nitrous oxide environment for nitridization, is proposed. The conventional method improves the hot carrier resistance of devices and suppresses the penetration of doped ions from the subsequently formed gate to the gate oxide layer. However, by this technique, fixed oxide charges which affect the electrical characteristics of gate oxide are caused, and a maximum mobility degradation is reached. Furthermore, the high temperature treatment of nitridation is very complicated, and therefore, a nitrous oxide layer with a high quality is difficult to obtain.
Another way of enhancing the reliability of a gate oxide layer is proposed in "Highly Reliable 0.15 .mu.m MOSFETs Surface Proximity Gettering (SPG) and Nitrided Oxide Spacer Using Nitrogen Implantation" in "1995 Symposium on VLSI Technology Digest of Technical paper", p. 19-20 by T. Kuroi et. al.. In this method, after a spacer is formed, nitrogen ion implantation is performed to improve the quality of spacer oxide layer, and thus, enhance the reliability of products. However, this technique cannot prevent the hot carrier degradation caused in the interface between the silicon oxide layer and the silicon substrate at the corner of the gate oxide layer near the spacer.